1986 automatic transmission in a Ford Ranger won't go into gear

It's dead. What you witnessed was the transmission in its death throes. Now the question is, do you want to rebuild the transmission or say a prayer and place the remains in the bone yard and let other old Rangers live on with its transplanted parts.

Check fluid?may be out,if you are lucky,but being that year model,low fluid would kill it,as Bmark said above.